Aircraft and other passenger transport vehicles typically have on-board lavatories with vacuum toilet systems. These systems typically include a waste-receiving toilet bowl connected to a main waste tank via a sewer pipe or main waste line. A discharge or flush valve is typically mounted on the sewer pipe to selectively allow fluid communication between the toilet bowl and the main waste tank. To power the toilet system, the waste reservoir is maintained under a pressure that is substantially lower than the pressure in the waste-receiving toilet bowl, which is typically under the near-atmospheric pressure of the aircraft's passenger cabin. Thus, when the discharge valve is opened, the pressure differential between the bowl and the reservoir causes the waste in the bowl to be drawn through the pipe into the waste reservoir.
The vacuum created for the flushing action may either be via one or more vacuum pumps, or, in the case of an aircraft in flight, via a pressure differential. For example, aircrafts typically have a vacuum disposal system that applies a vacuum to pull waste media and flush water/spent water from toilets and/or sinks into an on-board waste water storage tank. The suction is generated either by the pressure differential between the pressurized cabin and the reduced pressure outside of an aircraft at high flight altitudes or by a vacuum generator at ground level or at low flight altitudes.
In vacuum waste systems, this differential pressure is what drives the collected mixed media (which can be solid and/or liquid human waste along with other waste items, such as paper products) from the toilet bowl into an accumulation point. The discharge valve should provide an interface for such a vacuum system without venting the pressure differential completely. It should also allow for the controlled addition of material into the ambient-pressure environment, while providing a leak-free obstruction that can be moved or rotated in a controlled manner so as to allow for the passage of waste from the ambient-pressure environment (e.g., the toilet bowl) to the low pressure environment (e.g., the waste tank). The discharge valve is then returned to its closed position in order to prevent further movement of media and/or waste into the waste tank until the next flush is activated.
Although efficient, vacuum toilets create a loud noise level during the flush cycle, due to the amount of vacuum that needs to be applied in order to cause the septic waste to travel from the toilet basin to the holding tank. The loud flushing sound is created when the flush valve opens. The differential pressure forcefully draws the waste down the drain, and the pressure differential must be large enough to cause the waste to flow the entire distance from the toilet basin to the septic holding tank.
Because the main holding tank can be located quite far from the lavatory, the assignee of the present application has developed a two-stage flush system that uses an intermediate holding tank or reservoir. Aspects of this design are described in co-pending U.S. Ser. No. 13/804,539 titled “Two-Stage Flush and Grey Water Flush Systems and Devices.” The intermediate tank described in that application functions as a transient tank between the toilet bowl and the main waste tank. It is generally positioned in fluid communication with the toilet bowl. In some embodiments, the intermediate tank is positioned beneath the toilet bowl in the lavatory plumbing. A first valve controls the flow from the toilet to the intermediate holding tank. A second valve (or valve system) controls the flow from the intermediate holding tank to the main waste tank. Improved features for either the first and/or the second valve or second valve system are provided herein. The embodiments described herein, however, may also be used with a system that employs a single flush that delivers waste directly from the toilet basin to the main